Enhanced biodegradation of 17α-ethinylestradiol by rhamnolipids in sediment/water systems

Environmental context The steroid hormone 17α-ethinylestradiol (EE2) has been established as a highly estrogenic substance, which potentially causes serious harm to environmental health. Rhamnolipids are a widely researched glycolipid used for the degradation of organic pollutants. Therefore, this study focused on the change of biodegradation of EE2 affected by rhamnolipids in sediment/water systems, showing increased and more rapid degradation. Abstract Rhamnolipids can enhance the remediation of hydrophobic organic pollutants in the environment. However, the rhamnolipid-associated biodegradation of hormones has rarely been investigated. In this study, aerobic biodegradation shake-flask experiments were conducted to investigate biosurfactant-associated biodegradation of 17α-ethinylestradiol (EE2) in sediment/water systems and to assess how the biodegradation rate is influenced by rhamnolipids produced by Pseudomonas aeruginosa MIG-N146. Results showed that EE2 biodegradability is significantly increased with increasing rhamnolipid concentration. An improved pseudo-first-order kinetic equation was established to simulate enhanced EE2 biodegradation at varying rhamnolipid concentrations. The biodegradation rate (k) initially increased marginally, and then increased rapidly with rhamnolipid concentrations exceeding the effective critical micelle concentration. The degree of enhancement of organic biodegradation was mainly affected by organic mass transfer, owing to rhamnolipidic micellar solubilisation, and by rhamnolipids acting as a primary substrate to stimulate the microbial consortium. Analysis results through various techniques indicated the formation of three main types of metabolic intermediates, with diverse polarity and biodegradability characteristics, in the process of EE2 biodegradation. Thus, it was concluded that the presence of rhamnolipids did not negatively affect the processes of EE2 biotransformation by indigenous microorganisms in the original sediment/water systems. This study presents an effective potential application of rhamnolipidic surfactants for enhancement of EE2 biodegradation in sediment/water systems.